1. Field of the Invention
The present invention relates to a sheet processing apparatus for processing sheets and an image forming apparatus having the sheet processing apparatus in an apparatus main body.
2. Related Background Art
Conventionally, the apparatus main body of an image forming apparatus for forming images on sheets may be equipped, for example, with a sheet processing apparatus for stapling sheet bundles. Examples of the sheet processing apparatus are disclosed in Japanese Patent Application Laid-Open No. H11-348451 and Japanese Patent Application Laid-Open No. 2000-169028.
In the sheet processing apparatus disclosed in Japanese Patent Application Laid-Open No. H11-348451, a saddle stitching stapler serving as a first sheet processing unit for stapling a middle portion of a sheet bundle and a side stitching stapler serving as a second sheet processing unit for stapling an end portion of a sheet bundle are arranged so as to be spaced apart from each other in a sheet bundle conveying direction. The saddle stitching stapler and the side stitching stapler move in a width direction of a sheet bundle to staple the sheet bundle.
In the sheet processing apparatus disclosed in Japanese Patent Application Laid-Open No. 2000-169028, an end portion and the middle portion of a sheet bundle are selectively stapled by one stapler.
In general, a sheet bundle stapled at an end portion is not folded, so the number of sheets in such a sheet bundle can be large. Thus, in a side stitching stapler, a staple driving portion for driving staples into a sheet bundle and a staple clinching portion for receiving distal ends of staples protruding from the back surface of the sheet bundle and folding them, are pivoted so as to be capable of opening and closing, thereby achieving a firm structure.
Meanwhile, a sheet bundle stapled at a middle portion is folded for bookbinding, so the number of sheet contained therein is smaller than that in the case of a sheet bundle stapled at an end. Thus, the structure of a saddle stitching stapler is not so firm as that of a side stitching stapler. Further, in a saddle stitching stapler, in order to be capable of receiving a middle portion of a sheet bundle, the staple driving portion and the staple clinching portion are separated from each other, so it is rather difficult to attain a firm structure.
In the sheet processing apparatus disclosed in Japanese Patent Application Laid-Open No. H11-348451, a side stitching stapler and a saddle stitching stapler are selectively used according to a position where a sheet bundle is stapled. Thus, it is possible to staple an end portion of a sheet bundle containing a large number of sheets by the side stitching stapler. However, in the sheet processing apparatus disclosed in Japanese Patent Application Laid-Open No. H11-348451, two staplers are arranged so as to be spaced apart from each other in the sheet conveying direction, resulting in a rather large apparatus size.
Further, in the sheet processing apparatus disclosed in Japanese Patent Application Laid-Open No. H11-348451, in which two staplers are arranged so as to be spaced apart from each other in the sheet conveying direction, it is necessary to provide a drive source for moving the staplers in the sheet bundle width direction for each stapler, resulting in a rather large apparatus size.
In contrast, in the sheet processing apparatus disclosed in Japanese Patent Application Laid-Open No. 2000-169028, side stitching and saddle stitching are effected by a single stapler, so it is possible to achieve a reduction in apparatus size. However, for saddle stitching, the stapler is separated into a staple driving portion and a staple clinching portion, and, when stapling an end portion of a sheet bundle, it may occur that a sheet bundle with a large number of sheets cannot be stapled. In view of this, in the sheet processing apparatus disclosed in Japanese Patent Application Laid-Open No. 2000-169028, it might be possible to form the stapler in a firm structure, which, however, would lead to an increase in apparatus size which is another problem.
Japanese Patent No. 3215909 discloses a construction in which a sheet delivery unit and two side stitching staplers are formed into an integral unit on a movable board and in which the integral unit is caused to slide on a stationary board due to a slide rail and a slide roller by a drive force of a stepping motor. However, the staplers disclosed in Japanese Patent No. 3215909 are incapable of saddle stitching. Further, in the construction disclosed in Japanese Patent No. 3215909, it is impossible to form a side stitching stapler and a saddle stitching stapler into an integral unit.
Thus, there has been a demand for a sheet processing apparatus which is of a small size and which can reliably perform both side stitching and saddle stitching. Further, a similar problem is involved in a sheet processing apparatus for perforating a sheet bundle.
Further, an image forming apparatus equipped with such a sheet processing apparatus is inevitably of a large size.